In the past year, we have made important progress in our understanding of the mechanism of action of a class of regulatory RNAs that respond to amino acid starvation in a variety of bacteria, including clinically important pathogens of genera such as Bacillus and Listeria. The T-box riboswitches control the expression of aminoacyl-tRNA synthetases, the enzymes responsible for specific charging of tRNA with amino acids, in response to intracellular amino acid levels in Gram-positive bacteria. It is essential for cell survival and virulence. Although this mRNA domain was discovered in 1993, it was not until our work published lst year that the mechanism by which the T-box specifically recognizes tRNA was elucidated. This year, we have uncovered the mechanism employed by the RNA to evaluate the aminoacylation (charge) state of tRNA, allowing it to respond to starvation. We have also explored the molecular underpinnings for the ability of the glmS ribozyme-riboswitch to control bacterial cell wall biosynthesis.